1. Field of the Invention
The present invention generally relates to a technique of using an inductive recording head to store information onto a magnetic medium, and in particular to circuits for reducing the current reversal time of the current through the inductive recording head for write drivers having an H-type configuration.
2. Description of the Related Art
Typically, a conventional H-type current write driver drives a magnetic recording head via a suspension interconnect. Because of the relatively low data rates, the current reversal times in the magnetic recording head are relatively large with respect to the echo-return time (e.g., twice the xe2x80x9ctime of flightxe2x80x9d of the interconnect) which, for an industry standard interconnect in a 3.5 inch drive has a length of 5 cm, is approximately 500 picoseconds. As a result, when the next current reversal arrives at the head, the echoes of the previous current reversal have dissipated enough not to cause a noticeable transition shift in the written data.
However, the ever increasing data rates require the current reversal time to be much smaller now to allow for the lower minimum time interval T between two adjacent current reversals commensurate with the higher data rate (e.g., T=1/DR, where DR is data rate in bits/sec). This minimum time interval is a so-called xe2x80x9cbit cell time windowxe2x80x9d. With these higher data rates, T is becoming so small that the echoes of a previous current reversal may not have dissipated enough at the next current reversal, thereby causing a timing shift in the written data (timing distortion).
The conventional write configuration is illustrated in FIG. 1(a), and includes a write driver 10, an interconnect 12 typically of the integrated lead suspension (ILS) type and having characteristic impedance ZO, and a magnetic recording head 14 having write current IW and equivalent inductive element Lh and resistive element Rh. A cross section of the ILS type of interconnect is illustrated in FIG. 1(b).
The write driver 10 is configured in an xe2x80x9cHxe2x80x9d topology with the write head 14 at the cross-bar of the xe2x80x9cHxe2x80x9d. When a data pulse is of one polarity the pair of switches S are closed to permit current flow in one direction in the write head. An opposite polarity data pulse causes switches S_bar to close to permit current flow in the opposite direction in the write head.
As illustrated in the cross-sectional view of FIG. 1(b), the ILS structure typically includes a stainless steel suspension 12a, and traces 12b, 12bxe2x80x2 separated by dielectric 12c, typically polymide with a typical dielectric coefficient ∈r≈2.7. Traces 12b, 12bxe2x80x2 have a typical separation of 50 xcexcm and line width perhaps slightly larger. The signal power travels predominantly between trace 12b and the stainless steel suspension 12a and between trace 12bxe2x80x2 and the suspension 12a. The signal power transfer by the transmission path formed by the 12b and 12bxe2x80x2 trace can be neglected. Therefore, the two transmission lines in FIG. 1(a) (each with a single-ended characteristic impedance Z0/2, half the differential characteristic impedance Z0 of the ILS) are an adequate representation of the ILS.
In the conventional systems, it is also known to source-terminate the ILS with an impedance substantially equal to the characteristic impedance of the ILS in order to absorb the reflections coming from the write head Because these reflections are no longer reflected back to the write head, they do not upset the timing of subsequent current reversals in the write head. FIG. 2(a) shows a conventional source-terminated current write driver including impedance matching resistors 20. FIG. 2(b) shows a conventional source-terminated voltage write driver.
The disadvantage of this conventional characteristic source termination scheme is that the achievable write head current reversal time is now determined by the inductance of the write head and the characteristic impedance of the ILS:
t10,90%=2.2Lh/(ZO+Rh), 
where t10,90% is the reversal time interval from 10% to 90% of the steady state signal levels. Lh is the head inductance; and Rh is the head resistance.
As a result, using the rule of thumb that the bit cell time window T must be equal or larger than 2xc2x7t10,90%, the maximum achievable data rate is given by:
Data Ratemax=(ZO+Rh)/4.4Lh[bits/sec]
With Lh=40 nH, Rh=15 xcexa9 and ZO=70 xcexa9, a maximum data rate is found of 480 Mbits/sec, or 60 Mbytes/sec.
To improve on this data rate, the characteristic impedance of the ILS could be made higher and/or the inductance of the head could be reduced. However, increasing the characteristic impedance of the ILS is difficult because the width of the traces becomes disappearingly small (for acceptable tolerances in the characteristic impedance of these lines about 80 xcexa9 seems to be the maximum achievable impedance given the materials and dimensions used) Lowering the head inductance without increasing the write current to excessive levels has shown to be difficult. Such excessive write currents would require large area transistors in the write driver, associated with larger parasitics. This would slow down the write driver.
In view of the foregoing and other problems, it is, therefore, an object of the present invention to provide a structure and method for improving the write speed of an inductive recording head.
It is another object of the invention to achieve the shortest possible time interval between two write current reversals in an inductive recording head, as determined to be the current reversal time of the magnetic write head.
It is yet another object of the invention to achieve this shortened time interval by eliminating transition shift (e.g., timing distortion) in the written data caused by the reflections traveling along the interconnect between the write head and the write driver.
It is another object of the invention to achieve this shortened time interval by overcoming the limitation placed on the current reversal time by a relatively large ratio of head inductance and characteristic impedance of the interconnect by temporarily enlarging the source strength of the write driver immediately following each current reversal.
It is still another object of the invention to achieve the write driver source strength enlargement using a spiking circuit based on a current mirror circuit.
It is another object of the invention to reduce the write current reversal time by compensating for skin-effect losses in an Integrated Lead Suspension (ILS) type of interconnect between the write driver and the write head.
It is yet another object of the invention to achieve this skin-effect compensation by increasing the resistance value of the termination resistors used for suppressing echoes returning from the magnetic write head above the theoretical value.
In a first aspect of the present invention, a magnetic recording circuit is disclosed, having a magnetic write head receiving an input write signal having a first amplitude, and an enhancement circuit increasing a signal strength at the input of the magnetic write head above that first amplitude for a predetermined time interval immediately after every polarity reversal, where the predetermined time interval representing a transition period of the magnetic write head, defined as a time period for a current through the magnetic write head to reach a substantially steady state value following a polarity reversal
In a second aspect of the present invention, a magnetic recording circuit is disclosed having a magnetic write head receiving an input write signal having a first amplitude, a write driver output stage providing the write signal as an output, the write driver output stage including a source-side termination circuit having output impedance ZS, and an interconnect circuit having an input, an output, and a characteristic impedance ZO, where the input of the interconnect circuit is coupled to the write signal output of the write driver output stage and the output of the interconnect circuit is coupled to the write signal input of the magnetic write head, and where ZS=xcex1xc2x7ZO, 1xe2x89xa6xcex1xe2x89xa61.3.
In a third aspect of the present invention, a method is disclosed of increasing a data write rate in an inductive recording head by reducing a shortest possible write time interval between adjacent input data signal polarity reversals, including enhancing a signal strength at an input of the inductive recording head for a predetermined time interval after every polarity reversal, where the predetermined time interval is a transition period of the magnetic write head representing a time period for a current through the magnetic write head to reach a substantially steady state value following the polarity reversals.
In a fourth aspect of the present invention, a magnetic recording circuit is disclosed including a write driver output stage providing a write signal output with a write signal source strength SO, the write driver output stage including a source-side termination circuit having output impedance ZS, a magnetic write head having a write signal input essentially equal to strength SO, and an interconnect circuit having an input, an output, and a characteristic impedance ZO, the input of the interconnect circuit being coupled to the write signal output of the write driver output stage and the output of the interconnect circuit being coupled to the write signal input of the magnetic write head, where source strength SO of the write driver at the input of the interconnect circuit, is temporarily increased for a predetermined time duration xcex94t after every polarity reversal of the write signal.
In a fifth aspect of the present invention, a magnetic recording apparatus is disclosed including a magnetic write head receiving an input write signal having a first amplitude, and an enhancement circuit increasing a signal strength at the input of the magnetic write head above that first amplitude for a predetermined time interval after every polarity reversal, where the predetermined time interval is a transition period of the magnetic write head representing a time period for a current through the magnetic write head to reach a substantially steady state value following a polarity reversal.
In a sixth aspect of the present invention, a magnetic recording apparatus is disclosed including a magnetic write head receiving an input write signal having a first amplitude, a write driver output stage providing the write signal as an output, the write driver output stage including a source-side termination circuit having output impedance ZS, and an interconnect circuit having an input, an output, and a characteristic impedance ZO, the input of said interconnect circuit being coupled to the write signal output of the write driver output stage and the output of the interconnect circuit being coupled to the write signal input of the magnetic write head, and where ZS=xcex1xc2x7ZO, 1xe2x89xa6xcex1xe2x89xa61.3.
Thus, the present invention achieves the shortest possible time interval between two adjacent write current reversals in an inductive recording head by eliminating a transition shift (timing distortion) in the written data caused by the reflections traveling along the interconnect between the write head and the write driver using the uninterrupted source-termination of the write driver and overcoming the limitation placed on the current reversal time by a relatively large ratio of head inductance and characteristic impedance of the interconnect by temporarily enlarging the source strength of the write driver immediately following each current reversal. The shortest possible time interval, i.e., highest achievable data rate, is then only limited by the current reversal time that can be achieved with this temporarily enlarged source strength.
Further, with the invention, a method and circuitry are provided to increase the data rate beyond the above mentioned limitation by xe2x80x9cspikingxe2x80x9d the driver""s source strength during the current reversals while maintaining, without interruption, the write driver source-terminated to the characteristic impedance of the ILS to suppress any echoes returning from the magnetic write head.